4.9t^2+24.5t-21=0

Solution for 4.9t^2+24.5t-21=0 equation:

4.9t^2+24.5t-21=0

a = 4.9; b = 24.5; c = -21;
Δ = b2-4ac
Δ = 24.52-4·4.9·(-21)
Δ = 1011.85
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(24.5)-\sqrt{1011.85}}{2*4.9}=\frac{-24.5-\sqrt{1011.85}}{9.8}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(24.5)+\sqrt{1011.85}}{2*4.9}=\frac{-24.5+\sqrt{1011.85}}{9.8}
$